In recent years, the functions and performance of various types of electronic equipment and communication equipment have been improved by using digital circuits and by employing higher in step with a remarkable progress of or improvements in semiconductor technologies. Inductors used in such various equipment are required to have much smaller dimensions like miniature chip type inductors and Yet higher reliability.
Prior art chip inductors will be explained in the following:
FIG. 13 is a perspective view of a typical prior art chip inductor showing its internal structure. In FIG. 13, a drum type bobbin 51 having a round flange on each end thereof attached by an adhesive 54 to two external terminals 53, each of which has an internal connection terminal 52. The bobbin 51 is formed of ferrite, ceramics or resin. A winding 55 is disposed around the bobbin 51, and one end of the winding 55 is attached to the internal connection terminal 52 by wrapping, and further, with solder 56 being applied over the wrapping portion for secure connection. An exterior enclosure 57 made of insulating resin or the like encases the whole above structure except for the external terminals 53.
FIG. 14 is a perspective view of another typical prior art chip inductor showing its internal structure. In FIG. 14, a bobbin 51 and an external terminal 53 are put together by insert-molding. The rest of the structure is the same as shown in FIG. 13.
With the foregoing prior art structures, because of the drum type bobbin 51 having a round flange at both ends, there is much dead-space left within the outline contour containing the exterior enclosure 57, thereby imposing a limit on miniaturization. Particularly, when the drum type bobbin is attached to the external terminals 53, slippages in the mutual positions are likely to take place and some extra space has to be set aside for the possible displacement, thereby causing this structure not to be so suitable for the miniaturization of chip inductors.
Besides, because the beginning and ending of the winding 55 are located on the same flange, the distribution capacitance between wound wires tends to increase extremely with a chip inductor of a small number of wire turns, resulting in the deterioration of Q-Factor characteristics.
Also, the flange of the bobbin, at the side where the internal connection terminal 52 exists, is covered by the internal connection terminal 52 which is serving as a magnetic shield. As a result, magnetic fluxes are interrupted and Q-Factor characteristics are further deteriorated.
Further, when the bobbin is made of ferrite or ceramics, it has not been easy to produce the bobbin to required shapes, since the configurations of the bobbin are usually rather complex.